I think the drink through...
I did this last night when I was deciding NOT to buy a beer before I got on the train after work.
The AV said all the things you mentioned -- "oh it's just one," "who cares anyway," etc.
But I focused on remembering why I was quitting. I knew it wouldn't be just one. One beer last night would've led to me getting falling down drunk at some future point, maybe not tomorrow, maybe not next week, but sometime in the future. I KNOW this now, because I've tried and failed at moderation enough times that I'm 100% sure it's not going to work for me.
So before you take that first drink, I guess my advice is to think through where it's likely to lead you, not just in the immediate future, but later on as well.